The clustering and subsequent processing of integral plasma membrane proteins by monospecific antibodies will be studied on cultured animal cells. Fluorescent labeled antibodies will be employed to identify cytoskeletal proteins involved in transmembrane linkages to induced membrane clusters. Single and double label transmission electron microscopic studies will determine the sequence of structural association produced as the clusters are internalized. The endocytosis of clusters by both smooth and coated vesicles will be analyzed to see if these two morphologically distinct uptake systems lead to two distinct cytoplasmic targets and fates. Biochemical experiments will analyze the effect of clustering a single membrane protein on its turnover. Latex beads linked to specific antibodies will allow the isolation of membrane fragments containing clusters at different stages in the processing sequence for the identification of intergal and peripheral proteins that become associated with clusters as they are processed. The use of latex beads with specific antibodies will provide direct correlations between these structural and biochemcial observations. Receptor mediated uptake by smooth vesicles on fibroblasts was previously unknown. A comparison of smooth to coated vesicle uptake will expand understanding of the mechanisms of both endocytic systems and their significance for membrane turnover, transmembrane signalling, and transport.